For many years there has been a desire to provide, for instance, an autonomous apparatus for floor treatment, particularly a vacuum cleaner, which is controlled by a sensing system sweeping around the horizon in analogy, for example, with a ship radar. Then the desire is, that the apparatus should be able to orientate itself in a room, such that it, for instance, will be able to perform a cleaning function according to a predetermined pattern or a predetermined strategy and at the same time avoid colliding with different obstacles, which may be arranged in the room, besides avoiding collisions with the walls of the room.
The patent document SE 313,409 from 1969 discloses a device for an independently operating apparatus for floor treatment, which is provided with a pair of wheels driven by an electric motor. This device is characterized in that one of the wheels is automatically releasable against the action of a spring when the apparatus meets an obstacle, whereby the pair of wheels may be turned around a vertical axis, and the moving direction of the apparatus may be changed and additionally the direction of wheel rotation may be switched so that the apparatus in principle can move and avoid the obstacle. Additionally, the device is guided by a controller, which generally guides the travel of the device over the surface to be cleaned.
Also the document SE 364,574 discloses a corresponding device, which on its front side is provided with an obstacle detection device having sensing means-delivering electric signals and by which the width of obstacles, in the course of the device, may be determined. The sensing means operate completely mechanically and preferably consist of micro-switches.
In GB 1,403,860, having priority from an 1972 application, is disclosed a process and a device for automatic treatment, e.g., cleaning, of a bounded area, whereby the device will move over the entire area and automatically changing its course at the area boundaries. Anyhow, the device cannot in advance detect other obstacles present within the bounded area and follows in principle a predetermined program to cover all the surface of the bounded area.
Another such apparatus system is further disclosed in the document CH 619,799 from 1973, having priority in an application DE 2,364,002 from 1973. This apparatus, which is driven by two wheels, is arranged with an electro-optical measuring device, which displays several beam inputs and outputs. The measuring device serves to measure the distances between the apparatus and measuring points on the walls limiting the room. The measured points are entered into a coordinate calculation processor, which calculates, correlates and controls, respectively, the coordinates of the measuring points and stores these calculated values in an orientation memory. By means of a path counter connected to the wheels the motion of the apparatus is additionally calculated and the apparatus is guided by means of this information to by itself systematically travel over the entire surface of the floor for cleaning that surface.
A drawback here is the difficulty to locate obstacles which may be present in the course of the apparatus in its travels over the floor as an electro-optical sensing system which, due to the high propagation speed, demands a measuring system capable of measuring very short time periods, why, first of all, such a system, even still with the recent development taken place within electronics and computer technique, will be so expensive that it above all from the point of price level cannot be made available to the public. Thus, it is still technically seen difficult with such an electro-optical method to measure short distances with a satisfactory resolution. Additionally, if an obstacle exhibits a smooth angled surface, such an electro-optical sensing pulse may well be reflected in such a direction, that the reflected signal never will be apprehended by the receiver and thereby no indication of the obstacle will be obtained, why the apparatus will soon collide with such an obstacle in its travel.
In an document from 1984 by James L. Crowley having the title "Position Estimation for Intelligent Mobile Robot", The Laboratory for Household Robotics, Carnegie-Mellon University, a solution of the problem to maintain an estimate of the position of the robot, when it travels in either a known or unknown environment, is further described. The document additionally gives a number of further references to different algorithms used for modelling in this context and which may be used to program a dataprocessor for the guiding of such a robot. An apparatus demonstrated in the document utilizes in part encoders at the robot's wheels to determine its travel and in part a rotating sensor sensing the distance to exterior surfaces having a beam with a starting diameter of approximately 7.5 cm and a beam spread of about 3.degree.. The sensor rotates at about 1 revolution per 5 seconds and returns the distance to the nearest surface within 6 m to a resolution of 3 cm. The apparatus may then be placed into a learning mode during a guided tour of the world where it is supposed to act. Starting from the learn mode the apparatus will then from some starting point by itself orientate in this now explored environment.
In U.S. Pat. No. 4,674,048 having priority from JP 200360/83 is disclosed a guiding system for a moving robot, which calculates its momentary position and sequentially stores data of the obtained positions and which information then is used for the continuing travel of the robot. The robot then calculates a travel pattern within a specified area, whereby it is allowed to travel within the range without leaving any region untravelled and taking notice of possible obstructions which alters its course. Besides the robot compensates position errors due to slippage of its drive wheels or errors in the operation of its motors.
There are additionally a multitude of other documents like for example U.S. Pat. Nos. 4,114,711 (1978), 4,700,424 (1987), 4,887,415 (1989) which also disclose different arrangements in automatically guided autonomous machines.
Another document from 1987, U.S. Pat. No. 4,638,445 discloses a vision system for a mobile robot which employs at least two arrays of sensors for obtaining data on the position and distance to objects in a workspace. One sensor array looking downwards is used principally to see near objects and the other array is used principally to see far objects. The device utilizes ultrasonic transducers which then operate as monostatic sensors. The system sketched demands a fairly large and even high device not suitable for an autonomous apparatus for floor treatment, particularly a vacuum cleaner.
Finally a recent document U.S. Pat. No. 5,111,401 issued 1992 discloses a navigational control system to direct an autonomous vehicle to travel along a floor from a first location to a destination within an environment. The vehicle relies on at least one reflective encoded stripe applied to the floor. The navigation also relies on a separately installed host computer via a wireless link, which together with a local processor in the vehicle guides the vehicle.
Common to all these previous designs is that those because of the multitude of differently combined methods needed for their orientation and steering most often will be of a clumsy size and above all they are utterly complicated and expensive to produce.
Therefore there is a desire to provide a method which may be applied in a system of an autonomous device, which by way of this method still will be possible to manufacture at reasonable production costs, such that a ready-made product, for instance, for automatic vacuum cleaning of a room will be provided at a total price, which makes the product available to the public.